1. Field of the Invention
The present invention relates to a semiconductor device configured to detect magnetism, and a method of manufacturing the semiconductor device. More particularly, the present invention relates to a semiconductor device capable of detecting magnetism in two-dimensional or three-dimensional directions with high sensitivity by including a plurality of Hall elements and a magnetic body that is configured to converge magnetic fluxes passing near the semiconductor device, and to a method of manufacturing the semiconductor device.
2. Description of the Related Art
Semiconductor devices configured to detect magnetism by the Hall effect have been known for years, and semiconductor devices that combine a Hall element with a magnetic body have also been made in order to enhance sensitivity and performance and detect magnetism in two-dimensional or three-dimensional directions.
For instance, in a magnetic field direction sensor utilizing the Hall effect that is described in Japanese Patent Application Laid-open No. 2002-71381, a plurality of Hall elements are arranged and a magnetic flux converging plate having a flat shape and made from a soft-magnetic material is arranged above a region of the plurality of Hall elements.
In the magnetic field direction sensor, an edge portion of the magnetic flux converging plate is located in the Hall element region, and magnetic fluxes converged by the magnetic flux converging plate accordingly concentrate in a direction perpendicular to the Hall elements in the vicinity of surfaces of the Hall elements. This makes the density of magnetic fluxes passing the Hall elements high, thereby enhancing the sensitivity of detecting the magnetic fluxes. This further enables the magnetic field direction sensor to calculate magnetic flux directions and the magnetic flux intensity in each magnetic flux direction by detecting and calculating for each of the plurality of Hall elements the intensity of a magnetic flux that passes the Hall element. A magnetic flux direction relative to the magnetic field direction sensor can thus be broken into coordinate axes that have the magnetic field direction sensor as the reference. A marked improvement in performance from a magnetic sensor that simply uses a Hall element can be expected as a result.
A magnetic sensor utilizing the Hall effect that is described in International Patent WO2007/119569 is based on a structure and principle similar to those of Japanese Patent Application Laid-open No. 2002-71381. Stress generated between the magnetic flux converging plate and a semiconductor substrate on which the magnetic flux converging plate is mounted due to the difference in material, in particular, stress due to the difference in thermal expansion influences sensor characteristics significantly. The magnetic sensor therefore has a structure for reducing the influence.
The magnetic sensor achieves this goal by employing a structure in which a base layer is formed between the magnetic flux converging plate and the semiconductor substrate, a portion of the base layer that is connected to the semiconductor substrate is smaller in area than the magnetic flux converging plate, and the base layer at least partially covers the Hall element region.
The magnetic sensor utilizing the Hall effect that is described in International Patent WO2007/119569 also regulates the shape in vertical cross-section of the magnetic flux converging plate, to thereby improve its performance.
FIG. 6A to FIG. 6C are diagrams for illustrating, as a magnetic sensor of the related art, the magnetic sensor that is described in International Patent WO 2007/119569. A main portion of the magnetic sensor is illustrated in vertical cross-section in FIG. 6A to FIG. 6C.
In the magnetic sensor illustrated in FIG. 6A, the base layer is smaller in area than the magnetic flux converging plate. Hall elements 102a and 102b are formed and embedded near one surface of a semiconductor substrate 101a. An insulating protective layer 103 is formed on surfaces of the Hall elements 102a and 102b. A base layer 104 is formed on a surface of the insulating protective layer 103 so as to cover the Hall elements 102a and 102b. A magnetic flux converging plate 105a is further formed on top of the base layer 104 from a magnetic material so as to be larger in area than the base layer 104.
Structures illustrated in FIG. 6B and FIG. 6C are tapered in a straight line in end surface directions of magnetic flux converging plates 105b and 105c. 
When the base layer or the magnetic flux converging plate is directly arranged on the Hall element region, stress is generated on the Hall element region, which is undesirable. Formation of the base layer, the magnetic flux converging plate, or other similar structures on the Hall element region should thus be avoided for the improvement of element performance as well.
In addition, the tapered structures of FIG. 6B and FIG. 6C do not exactly have a curvature that is preferred in order to converge magnetic fluxes efficiently and vertically to the Hall element region surface, which is formed in a direction parallel to the semiconductor substrate (planar direction). In a structure having the preferred curvature, an end surface of the magnetic flux converging plate faces the direction of the Hall elements, and a magnetic flux passing through a portion of the magnetic flux converging plate that is parallel to the semiconductor substrate is efficiently deflected in a direction perpendicular to the semiconductor substrate.
A magnetic sensor that includes a magnetic flux converging plate is fabricated by, as described in International Patent WO2007/119569 and Japanese Patent Application Laid-open No. 2008-55663, photolithography, vapor plating, and electrolytic plating. Shape regulation using a mold for electrolytic plating with a photoresist is employed as a method of forming the magnetic flux converging plates 105b and 105c, which are tapered in a straight line.
Another known method combines photolithography and electrolytic plating to form a plated object that has an approximate quadrant shape (see Japanese Patent Application Laid-open No. 2008-55663, for example).
According to this method, a structure having a curved surface that has an approximate quadrant shape in section can be formed by electrolytic plating.
It is not preferred to mount a base layer, a magnetic flux converging plate, or other similar structures on the Hall element region as described above, and there has been no effective measure to form a magnetic flux converging plate right above the Hall element region without forming a structure directly on the Hall element region.
There has also been a demand for a magnetic flux converging plate that has a more suitable structure for deflecting a magnetic flux vertically to the Hall element region, and for a method of manufacturing the magnetic flux converging plate.